In a typical chain transmission, a chain is in mesh with the teeth of a driving sprocket and one or more driven sprockets. In an automobile engine, for example, the timing chain transmits power from a sprocket on the engine crankshaft to one or more valve-operating camshafts. The chain is typically in sliding contact with several guides, one being a fixed guide in contact with the portion of the chain that travels in tension from a camshaft sprocket toward the crankshaft sprocket, and another guide being a movable guide, such as a pivoted tensioner lever, in contact with the portion of the chain traveling from the crankshaft sprocket toward a camshaft sprocket.
A typical roller chain or rollerless bushing chain is composed a first set of links each comprising a pair of opposed inner link plates connected by a pair of bushings, and a second set of links, each comprising a pair of opposed outer link plates connected by pins. The links of the first set are disposed in alternating relationship with the links of the second set, with each pin of a link of the second set extending through a bushing of a link of the first set. In the case of a roller chain, a roller is provided on the outside of each bushing. The link plates typically have flat upper and lower edges, extending in the direction of the length of the chain, and rounded ends, as shown in FIG. 6. The straight edges of the plates 400 come into sliding contact with the shoe surface Ga of a guide G over a relatively large area, with a resulting high friction loss, and increased fuel consumption when the chain is used as a timing chain. Other roller chains have gourd-shaped link plates, but even in the case of a chain having gourd-shaped plates, the area of contact with a guide is large enough to produce a significant friction loss.
In a chain described in Japanese Laid-Open Patent Publication No. 2003-176853, the upper and lower edges of the inner plates are farther than the upper and lower edges of the outer plates from a pitch line connecting the centers of the connecting pins. This chain construction reduces wear of the guide and reduces chain failure due to excessive forces applied at the locations at which the connecting pins are press fit into pin holes in the outer plates. However, because the inner plates have straight edges, they contact the guide over a large area, and the chain exhibits a high friction loss.
A principal object of this invention is provide an improved chain in which sliding friction between the chain and a guide is reduced. Other objects and advantages of the invention will become apparent from the following description.